Method for preparing low-aluminum iron phosphate from iron phosphate waste

Abstract

The invention belongs to the technical field of battery waste recovery, and provides a method for preparing low-aluminum iron phosphate from iron phosphate waste. The method comprises the following steps: mixing the iron phosphate waste, a first acid solution and water, and carrying out an acid dissolution reaction to obtain an acid solution; mixing an acid solution and ferric salt, adding hydrogen peroxide, and carrying out oxidation reaction until no ferrous iron exists in a reaction system, so as to obtain a blended oxidation solution; and mixing the prepared oxidation liquid with alkali liquor, carrying out primary aluminum removal to obtain primary aluminum-removed slag, mixing the primary aluminum-removed slag, second acid liquor and water, and carrying out secondary aluminum removal to obtain the low-aluminum iron phosphate. The method is simple, environmentally friendly and low in cost, deep removal of the aluminum impurities in the iron phosphate product is achieved, the low-aluminum iron phosphate with the aluminum impurity content as low as 0.02% or below is prepared, and the application prospect is quite wide.

Description

Technical Field

[0001] This invention relates to the field of battery waste recycling technology, and in particular to a method for preparing low-aluminum iron phosphate from iron phosphate waste. Background Technology

[0002] Lithium iron phosphate (LFP) batteries have been widely used in new energy fields such as electric bicycles, electric vehicles, and electric buses due to their low price and high safety. With the rapid development of the new energy industry, the amount of discarded LFP batteries is increasing year by year, making their efficient recycling a critical issue that urgently needs to be addressed. Currently, the recycling methods for LFP waste are mainly divided into two categories: one is direct regeneration of LFP waste; the other is the stepwise recycling to prepare lithium carbonate (or lithium hydroxide) and iron phosphate. In the latter method, an oxidative acid leaching process is typically used to selectively extract lithium, while iron and phosphorus are added to the leaching residue.

[0003] For leaching residues containing iron and phosphorus, existing recovery methods mainly employ high-concentration inorganic acids such as sulfuric acid and phosphoric acid for leaching, transferring iron and phosphorus to the liquid phase. Subsequently, ferric phosphate is precipitated by adjusting the pH with alkali. However, this method also dissolves aluminum impurities during the leaching process, resulting in a high aluminum content in the final ferric phosphate product, which adversely affects its electrochemical performance.

[0004] Therefore, developing a method for recovering and preparing low-aluminum ferric phosphate from ferric phosphate waste is of great significance. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing low-aluminum ferric phosphate using ferric phosphate waste, so as to solve the problem of high aluminum impurity content in ferric phosphate products prepared by existing recycling methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing low-aluminum ferric phosphate from ferric phosphate waste, comprising the following steps: 1) Mix the iron phosphate waste, the first acid solution, and water to carry out an acid dissolution reaction to obtain an acid solution; 2) Mix the acid solution and iron salt, then add hydrogen peroxide to carry out the oxidation reaction until there is no ferrous iron in the reaction system, and obtain the prepared oxidation solution; 3) Mix the prepared oxidizing solution and alkaline solution for the first aluminum removal to obtain preliminary aluminum-removed slag; mix the preliminary aluminum-removed slag, the second acid solution and water for the second aluminum removal to obtain low-aluminum iron phosphate.

[0007] Preferably, in step 1), the molar ratio of iron in the iron phosphate waste to hydrogen ions in the first acid solution is 1:3.0~3.8; and the mass ratio of the iron phosphate waste to water is 1:1~3.

[0008] Preferably, in step 1), the first acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0009] Preferably, the acid dissolution reaction in step 1) is carried out at a temperature of 25~120℃ for a time of 0.5~4 h.

[0010] Preferably, the molar ratio of phosphorus to iron in the oxidizing solution prepared in step 2) is 1:1.05~1.25.

[0011] Preferably, the iron salt includes one or more of ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, ferric nitrate, and ferrous nitrate.

[0012] Preferably, the oxidation reaction in step 2) takes 0.5 to 2 hours.

[0013] Preferably, the alkaline solution in step 3) includes one or more of sodium hydroxide solution, potassium hydroxide solution and ammonia water.

[0014] Preferably, in step 3), the pH value of the first aluminum removal is 1.65~2.05, the temperature is 20~60℃, and the time is 0.5~4 h.

[0015] Preferably, in step 3), the molar ratio of iron in the preliminary aluminum-removing slag to hydrogen ions in the second acid solution is 1:0.85~1.2; and the mass ratio of the preliminary aluminum-removing slag to water is 1:1~3.

[0016] Preferably, in step 3), the second acid solution includes one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0017] Preferably, the temperature for the second aluminum removal in step 3) is 70~100℃ and the time is 1~4 h.

[0018] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: This invention involves reacting ferric phosphate waste with acid and water to obtain an acid solution, then reacting the acid solution with iron salt and hydrogen peroxide to obtain a formulated oxidizing solution. The formulated oxidizing solution is then mixed with an alkaline solution for a first aluminum removal process, followed by a second aluminum removal process with the acid solution. This achieves deep removal of aluminum impurities from the recovered ferric phosphate product, resulting in the preparation of low-aluminum ferric phosphate.

[0019] The preparation method described in this invention is simple, environmentally friendly, and low in cost. The aluminum impurity content in the prepared low-aluminum iron phosphate is as low as 0.02%, and its application prospects are very broad. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 This is a process flow diagram of the present invention for preparing low-aluminum ferric phosphate using ferric phosphate waste; Figure 2 The XRD pattern of the low-aluminum anhydrous iron phosphate prepared in Example 1 is shown (the horizontal axis is the diffraction angle and the vertical axis is the diffraction intensity). Figure 3 The image shows a SEM image of the low-aluminum anhydrous iron phosphate prepared in Example 1. Detailed Implementation

[0022] This invention provides a method for preparing low-aluminum ferric phosphate from ferric phosphate waste, comprising the following steps: 1) Mix the iron phosphate waste, the first acid solution, and water to carry out an acid dissolution reaction to obtain an acid solution; 2) Mix the acid solution and iron salt, then add hydrogen peroxide to carry out the oxidation reaction until there is no ferrous iron in the reaction system, and obtain the prepared oxidation solution; 3) Mix the prepared oxidizing solution and alkaline solution for the first aluminum removal to obtain preliminary aluminum-removed slag; mix the preliminary aluminum-removed slag, the second acid solution and water for the second aluminum removal to obtain low-aluminum iron phosphate.

[0023] In this invention, the acid-soluble residue obtained from the acid dissolution reaction in step 1) can be washed to obtain commercially available carbon slag.

[0024] In this invention, the molar ratio of iron in the iron phosphate waste to hydrogen ions in the first acid solution in step 1) is 1:3.0~3.8, preferably 1:3.1~3.7, more preferably 1:3.2~3.5, and even more preferably 1:3.4; the mass ratio of the iron phosphate waste to water is 1:1~3, preferably 1:1.2~2.8, more preferably 1:1.5~2.5, and even more preferably 1:1.8~2.0.

[0025] In this invention, the first acid solution in step 1) preferably includes one or more of hydrochloric acid, sulfuric acid and nitric acid.

[0026] In this invention, the iron phosphate waste mentioned in step 1) preferably includes lithium iron phosphate battery waste, waste generated during the recycling of lithium iron phosphate battery waste, and waste generated during the production of iron phosphate.

[0027] In this invention, the temperature of the acid dissolution reaction in step 1) is 25~120℃, preferably 30~100℃, more preferably 40~80℃, and even more preferably 50~60℃; the time of the acid dissolution reaction is 0.5~4 h, preferably 0.8~3.5 h, more preferably 1.0~3.0 h, and even more preferably 1.5~2.5 h.

[0028] In this invention, the molar ratio of phosphorus to iron in the oxidizing solution prepared in step 2) is 1:1.05~1.25, preferably 1:1.08~1.20, more preferably 1:1.10~1.18, and even more preferably 1:1.12~1.15; the hydrogen peroxide is used to ensure that there is no divalent iron in the solution of acid solution and iron salt mixture.

[0029] In this invention, the iron salt preferably includes one or more of ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, ferric nitrate, and ferrous nitrate.

[0030] In this invention, the oxidation reaction time in step 2) is 0.5-2 h, preferably 0.7-1.8 h, more preferably 1.0-1.6 h, and even more preferably 1.2-1.5 h.

[0031] In this invention, the alkaline solution in step 3) preferably includes one or more of sodium hydroxide solution, potassium hydroxide solution and ammonia water.

[0032] In this invention, the pH value of the first aluminum removal in step 3) is 1.65~2.05, preferably 1.7~2, more preferably 1.75~1.95, and even more preferably 1.8~1.9; the temperature of the first aluminum removal is 20~60℃, preferably 25~55℃, more preferably 30~45℃, and even more preferably 35~40℃; the time of the first aluminum removal is 0.5~4 h, preferably 1~3.5 h, more preferably 1.5~3 h, and even more preferably 2~2.5 h.

[0033] In this invention, the molar ratio of iron in the preliminary aluminum-removing slag to hydrogen ions in the second acid solution in step 3) is 1:0.85~1.2, preferably 1:0.88~1.1, and more preferably 1:0.9~1.01; the mass ratio of the preliminary aluminum-removing slag to water is 1:1~3, preferably 1:1.2~2.8, more preferably 1:1.5~2.5, and more preferably 1:1.8~2.

[0034] In this invention, the second acid solution in step 3) preferably includes one or more of hydrochloric acid, sulfuric acid and nitric acid.

[0035] In this invention, the temperature of the second aluminum removal in step 3) is 70~100℃, preferably 75~95℃, more preferably 80~90℃, and even more preferably 85℃; the time of the second aluminum removal is 1~4 h, preferably 1.5~3.5 h, more preferably 2~3 h, and even more preferably 2.5 h.

[0036] In this invention, step 3) after the second aluminum removal preferably includes washing, drying, and calcination operations; the drying temperature is preferably 80~100℃, more preferably 85~95℃, and more preferably 88~90℃; the drying time is preferably 5~15 h, more preferably 6~12 h, and more preferably 8~10 h; the calcination temperature is preferably 550~750℃, more preferably 580~700℃, and more preferably 600~650℃; the calcination time is preferably 1~3 h, more preferably 1.5~2.5 h, and more preferably 2~2.2 h; the calcination is used to remove crystal water and convert it into anhydrous ferric phosphate.

[0037] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1

[0039] 1) Mix 800 g of ferric phosphate waste (phosphorus mass fraction of 16.74%, iron mass fraction of 28.77%, aluminum mass fraction of 0.26%) with 2400 g of water to form a slurry, then add 619 g of concentrated sulfuric acid. The molar ratio of iron in the ferric phosphate waste to hydrogen ions in the concentrated sulfuric acid is 1:3.0. React at 120℃ for 0.5 h, filter, and obtain an acid solution. 2) Mix 1 L of the acid solution obtained in step 1) with 27.5 g of ferrous sulfate heptahydrate, then add 12.45 g of hydrogen peroxide to carry out the oxidation reaction for 1.5 h until there is no ferrous iron in the system, and obtain the prepared oxidation solution (the molar ratio of phosphorus to iron in the prepared oxidation solution is 1:1.05). 3) Mix the prepared oxidizing solution obtained in step 2) with ammonia water until the pH value of the system is 1.65, and remove aluminum at 20℃ for 4 h. After filtration, a preliminary aluminum-removed slag is obtained. Mix 200 g of the preliminary aluminum-removed slag with 200 g of water to form a slurry, and add 22.1 g of concentrated sulfuric acid. The molar ratio of iron in the preliminary aluminum-removed slag to hydrogen ions in the concentrated sulfuric acid is 1:0.85. Remove aluminum at 100℃ for 1 h. Finally, filter, wash, dry at 80℃ for 15 h, and calcine at 650℃ for 2 h to obtain low-aluminum anhydrous ferric phosphate (denoted as anhydrous FePO4).

[0040] According to the test results, the low-aluminum anhydrous iron phosphate prepared in Example 1 contained 20.68% phosphorus, 36.26% iron, and 0.0084% aluminum by mass.

[0041] The XRD pattern of the low-aluminum anhydrous ferric phosphate prepared in Example 1 is shown below. Figure 2 As shown, from Figure 2 As can be seen, the obtained anhydrous ferric phosphate conforms to standard card PDF#29-0715. Its SEM image is shown below. Figure 3 As shown, from Figure 3 As can be seen from the results, the morphology of the obtained anhydrous iron phosphate is a spherical porous structure.

[0042] Example 2

[0043] 1) Mix 1000 g of ferric phosphate waste (phosphorus mass fraction of 10.07%, iron mass fraction of 17.34%, aluminum mass fraction of 0.17%) with 2000 g of water to form a slurry, then add 978 g of concentrated nitric acid. The molar ratio of iron in the ferric phosphate waste to hydrogen ions in the concentrated nitric acid is 1:3.4. React at 70℃ for 2 h, filter, and obtain an acid solution. 2) Mix 1 L of the acid solution obtained in step 1) with 80.3 g of ferric nitrate nonahydrate, then add 7.60 g of hydrogen peroxide to carry out the oxidation reaction for 0.5 h until there is no ferrous iron in the system, and obtain the prepared oxidation solution (the molar ratio of phosphorus to iron in the prepared oxidation solution is 1:1.15). 3) The prepared oxidizing solution and sodium hydroxide solution obtained in step 2) are mixed until the pH value of the system is 1.85, and aluminum is removed at 40°C for 2 h. After filtration, a preliminary aluminum-removed slag is obtained. 200 g of the preliminary aluminum-removed slag and 400 g of water are mixed and slurried, and 48.1 g of concentrated nitric acid is added. The molar ratio of iron in the preliminary aluminum-removed slag to hydrogen ions in the concentrated nitric acid is 1:1.01. Aluminum is removed at 85°C for 2.5 h. Finally, after filtration and washing, the mixture is dried at 90°C for 10 h and calcined at 750°C for 1 h to obtain low-aluminum anhydrous ferric phosphate.

[0044] According to the test results, the low-aluminum anhydrous iron phosphate prepared in Example 2 contained 20.62% phosphorus, 36.39% iron, and 0.0109% aluminum by mass.

[0045] Example 3

[0046] 1) Mix 1500 g of ferric phosphate waste (phosphorus mass fraction of 8.125%, iron mass fraction of 13.53%, aluminum mass fraction of 0.28%) with 1500 g of water to form a slurry, then add 1361 g of concentrated hydrochloric acid. The molar ratio of iron in the ferric phosphate waste to hydrogen ions in the concentrated hydrochloric acid is 1:3.8. React at 30℃ for 4 h, filter, and obtain an acid solution. 2) Mix 1 L of the acid solution obtained in step 1) with 21.5 g of ferrous chloride, then add 17.30 g of hydrogen peroxide to carry out the oxidation reaction for 2 h until there is no ferrous iron in the system, and obtain the prepared oxidation solution (the molar ratio of phosphorus to iron in the prepared oxidation solution is 1:1.25). 3) Mix the prepared oxidizing solution and potassium hydroxide solution obtained in step 2) until the pH value of the system is 2.05, and remove aluminum at 60℃ for 0.5 h. After filtration, obtain preliminary aluminum-removed slag. Mix 200 g of preliminary aluminum-removed slag and 600 g of water to form a slurry, and add 61.4 g of concentrated hydrochloric acid. The molar ratio of iron in the preliminary aluminum-removed slag to hydrogen ions in the concentrated hydrochloric acid is 1:1.2. Remove aluminum at 70℃ for 4 h. Finally, filter, wash, dry at 100℃ for 5 h, and calcine at 550℃ for 3 h to obtain low-aluminum anhydrous ferric phosphate.

[0047] According to the test results, the low-aluminum anhydrous iron phosphate prepared in Example 3 contained 20.54% phosphorus, 36.40% iron, and 0.0153% aluminum.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-aluminum ferric phosphate using ferric phosphate waste material, characterized by, The method comprises the following steps: 1) mixing iron phosphate waste, first acid liquor and water to perform acid dissolution reaction to obtain an acid solution; 2) mixing the acid solution with iron salt and adding hydrogen peroxide to perform oxidation reaction until there is no divalent iron in the reaction system to obtain a prepared oxidation liquor; 3) mixing the prepared oxidation liquor with alkali liquor to perform first aluminum removal to obtain a preliminary aluminum removal residue; mixing the preliminary aluminum removal residue, second acid liquor and water to perform second aluminum removal to obtain low-aluminum iron phosphate.

2. The method for preparing low-aluminum ferric phosphate using ferric phosphate waste according to claim 1, characterized by, In step 1), the molar ratio of iron element in the iron phosphate waste to hydrogen ion in the first acid liquor is 1:3.0-3.

8. The mass ratio of the iron phosphate waste to water is 1:1-3.

3. The method for preparing low-aluminum ferric phosphate from ferric phosphate waste according to claim 2, characterized in that, In step 1), the first acid liquor comprises one or more of hydrochloric acid, sulfuric acid and nitric acid. 4.The method for preparing low-aluminum ferric phosphate using ferric phosphate waste according to claim 3, characterized by, In step 1), the temperature of the acid dissolution reaction is 25-120℃, and the time is 0.5-4 h.

5. The method for preparing low-aluminum ferric phosphate from ferric phosphate waste according to any one of claims 1 to 4, characterized in that, In step 2), the molar ratio of phosphorus element to iron element in the prepared oxidation liquor is 1:1.05-1.

25. The iron salt comprises one or more of ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, ferric nitrate and ferrous nitrate. 6.The method for preparing low-aluminum ferric phosphate using ferric phosphate waste according to claim 5, characterized by, In step 2), the time of the oxidation reaction is 0.5-2 h. 7.The method of claim 6, wherein the low-aluminum iron phosphate is prepared by using the iron phosphate waste. In step 3), the alkali liquor comprises one or more of sodium hydroxide solution, potassium hydroxide solution and ammonia water.

8. A method for preparing low-aluminum ferric phosphate from ferric phosphate waste according to claim 7, characterized in that, In step 3), the pH value of the first aluminum removal is 1.65-2.05, the temperature is 20-60℃, and the time is 0.5-4 h. 9.The method of claim 7 or 8, wherein the low-aluminum ferric phosphate is prepared by adding the ferric phosphate waste material to a solution of phosphoric acid and a base, and then adjusting the pH of the solution to a range of 2 to 4. In step 3), the molar ratio of iron element in the preliminary aluminum removal residue to hydrogen ion in the second acid liquor is 1:0.85-1.

2. The mass ratio of the preliminary aluminum removal residue to water is 1:1-3. In step 3), the second acid liquor comprises one or more of hydrochloric acid, sulfuric acid and nitric acid. 10.The method for preparing low-aluminum ferric phosphate using ferric phosphate waste according to claim 9, characterized by, In step 3), the temperature of the second aluminum removal is 70-100℃, and the time is 1-4 h.

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